CD7, is the earliest T-cell antigen to appear during human T-cell ontogeny. Although the precise biological function of CD7 is unknown, there is evidence to suggest that CD7 is involved in T-cell ontogeny and T-cell activation. Thus, CD7 may play an important role during the process of T-cell development and function. In the present proposal, this possibility will be studied by examining the mechanisms with which CD7 mediates T-cell proliferation; furthermore, an animal model will be developed so that the function of CD7 can be analyzed in vivo. The specific aims are (1) to identify and study the molecules which interact with CD7 during T-cell activation, (2) to study the mechanisms with which CD7 functions, (3) to study the genomic organization of human and mouse CD7 and (4) to study the role of CD7 molecule in mouse T-cell function and ontogeny. To accomplished these goals, molecules which interact with CD7 are identified by co-immunoprecipitation and by chemical crosslinking experiments. Recombinant CD7 protein, produced in the baculovirus expression system, will be used to isolate these molecules. The functional domains of CD7 involved in these interactions will be characterized by site-directed mutagenesis. The interacting molecules will be affinity-purified for functional and molecular characterization. The signal transduction pathways utilized by CD7 will be identified with protein kinase inhibitors; the consequence of CD7-mediated T-cell activation will be determined by flow cytometric measurements of activation molecules and by analysis of gene transcription of lymphokines and proto-oncogenes. A restriction map of the human genomic CD7 will be determined and its nucleotide sequence determined. The organization and sequence of the mouse CD7 gene will be similarly analyzed. Monoclonal (mAb) and polyclonal antibodies to murine CD7 will be produced in hamsters using synthetic CD7 peptides as immunogens. The mAb's will be used to study the distribution of CD7 antigen during T-cell development and to the expression of CD7 during embryogenesis or during bone marrow reconstitution of SCID mouse. Finally, the disruption of coding region of the CD7 gene in transgenic animals will provide a powerful model to study the role CD7 in T-cell ontogeny and T-cell function.